While energy saving and compatible media are being expanded, heat fixing is the main method for fixing electrostatic image developing toner or ink-jet ink to a recording medium. However, for the purpose of improving operability, energy saving and expansion of compatible media types, there have been proposed systems in which fixing of the image is performed with an external stimulus different from heat. Among them, a light fixing system that is relatively compatible with the electrophotographic process has attracted attention, and several light-softened developers (light melting toners) have been reported.
The light melting toners described in Patent Document 1 (JP-A 2014-191077) and Patent Document 2 (JP-A 2014-191078) are characterized in that they contain a material (light phase transition material) that absorbs light and causes a phase transition from solid to liquid. However, there are very few reported examples of such light phase transition materials, the mechanism of the light phase transition is not sufficiently clarified, and the light softening mechanism of the light melting toner is also unclarified.
Further, the light phase transition material used in the toner described in Patent Document 1 and Patent Document 2 is an azobenzene derivative. It is known that an azobenzene derivative is a material that absorbs light and softens from the solid state (light phase transition). In addition, it is believed that the light phase transition of the azobenzene compound is caused by the crystal structure being broken by cis-trans isomerization.
However, the light melting toner reported at present has a problem that the productivity is low because the softening rate necessary for fixing is not sufficient.